Thin films for magnetic device

ABSTRACT

Methods are provided for forming uniformly thin layers in magnetic devices. Atomic layer deposition (ALD) can produce layers that are uniformly thick on an atomic scale. Magnetic tunnel junction dielectrics, for example, can be provided with perfect uniformity in thickness of 4 monolayers or less. Furthermore, conductive layers, including magnetic and non-magnetic layers, can be provided by ALD without spiking and other non-uniformity problems. The disclosed methods include forming metal oxide layers by multiple cycles of ALD and subsequently reducing the oxides to metal. The oxides tend to maintain more stable interfaces during formation.

RELATED APPLICATIONS

[0001] The present application claims priority under 35 U.S.C. §119(e)to provisional application No. 60/250,533, filed Nov. 30, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to magnetic structures for semiconductordevices and, more particularly, to a method for forming such structuresby depositing thin films using atomic layer deposition (ALD). Themagnetic structures may find use in magnetic random access memories(MRAMs) or in the magnetic field sensing elements that can be used inread-heads of computer hard-disk drives.

BACKGROUND OF THE INVENTION

[0003] Magnetic structures in integrated circuits and hard-diskread-heads include multi-layer devices comprising ferromagnetic films,conductive films and insulation films. These layered magnetic structuresinclude magnetic tunneling junctions, spin-valve transistors and pseudospin valves.

[0004] Most commonly, physical vapor deposition (PVD) and chemical vapordeposition (CVD) processes are used for deposition of these films. Thereare problems associated with these techniques; pinholes, film thicknessnon-uniformity and impurities at the film interfaces have caused devicesto fail. For example, PVD results in three-dimensional growth of cobaltinto islands on aluminum oxide, rather than two-dimensional film growth.In addition, ferromagnetic metals are rather sensitive to corrosion andthus require very careful treatment.

[0005] The problem of thickness non-uniformity can be mitigated using achemical-mechanical polishing technique (CMP). A CMP technique formaking a magnetic structure has been described in patent application WO00/38191, published Jun. 29, 2000. Unfortunately, CMP causes oxidationof some ferromagnetic materials. The oxygen must be removed and the filmrestored to elemental metal. This reduction reaction should be effectedat a low temperature (e.g., less than about 300° C.), as hightemperatures can destroy the functionality of the device.

[0006] Magnetic random access memories (MRAMs) have many desirableproperties. The magnetic polarity of the soft magnetic layer can beswitched very quickly, in as little as a nanosecond. The MRAM cells canbe packed close together; they can be scaled down to densities used forstate-of-the-art DRAMs (dynamic random access memories). MRAMfabrication requires fewer mask steps than DRAM fabrication, thussimplifying production and saving time and costs. In addition, the MRAMis non-volatile. Unlike the DRAM, it is not necessary to supply the MRAMwith continuous or periodic power. Once data has been written to theMRAM cell it will remain until it is rewritten and needs no additionalpower. Thus, it is expected that MRAMs have the potential to replaceDRAMs, static RAMs (SRAM) and flash memory in a wide range ofapplications, such as cell phones, MP3 players, personal digitalassistants (PDAs) and portable computers. The manufacturing of magneticcentral processing units (MCPU) will also be feasible. MCPUs can bereprogrammed on the fly to match any specific task. Before this canhappen, however, the remaining manufacturing problems of MRAM structuresmust be solved.

[0007] One form of a basic MRAM cell comprises a single current-sensingelement and a three-layer magnetically functional sandwich. These cellsare written to and read via current passing through adjacent conductinglines. In the sandwich a very thin, insulating or “tunnel dielectric”layer separates two magnetic layers. One of the magnetic layers is“soft,” which means that relatively small magnetic fields can change themagnetic polarity of the material, i.e., the material has lowcoercivity. The other magnetic layer is “hard,” which means that thepolarity of the material changes only under the influence of arelatively large magnetic field, i.e., the layer has high coercivity.The magnetic fields associated with writing and reading currents in theconducting lines cannot change the magnetic polarity of the “hard”magnetic layer. Data is written to the soft magnetic layer of thesandwich by passing a current through two conductor lines that areelectrically connected to the magnetic layers.

[0008] A single bit of data can be read from the sandwich by using anaddress line connected to one of the conductor lines. The address linecan turn on a sense transistor, depending on the current level thattunnels through the magnetic sandwich. The level of the tunnelingcurrent depends on the polarity of the magnetic layers in the sandwich.When the polarity of the magnetic layers is parallel, higher currenttunnels through the sandwich than when the polarity of the magneticlayers is antiparallel.

[0009] In the MRAM cell, the thickness of the insulating layer in thesandwich is in the nanometer range. The strength of the tunnelingcurrent through the insulator is very sensitive to the thickness of theinsulator. For example, aluminum oxide insulating thin films may be justfour atomic layers thick. Changing the thickness of the insulator byonly a tenth of a nanometer may change the tunneling current by an orderof magnitude. In addition, the insulator must have high dielectricstrength to withstand the operating voltages and provide sufficienttunneling current.

[0010] MRAM structures are also sensitive to pinholes in the layers.These can short-out the magnetic memory cell, rendering the devicenon-functional. The MRAM layers are also temperature sensitive; defectscan be expected if the layers are exposed to excessively hightemperatures.

[0011] The tunneling dielectric can be made, for example, by plasmaoxidizing an aluminum metal layer into aluminum oxide. Low surfacediffusion of atoms prevents formation of islands and pinholes.

[0012] Spin-valve transistors are used as magnetic field sensors.Read-heads for hard-disks and MRAMs can comprise spin-valve transistors.

[0013] In a typical spin-valve transistor structure (Sicollector/Co/Cu/Co/Pt/Si emitter), Co and Cu layers are deposited bysputtering. The optimum thickness of the Cu layer is about 2.0-2.4 nm.Improved flatness of the Co/Cu interface increases the magnetoresistanceeffect, which is desirable. The scattering probability of the hotelectrons in the base is altered by a magnetic field.

SUMMARY OF THE INVENTION

[0014] According to a first aspect of the invention, magnetic structurescomprising very thin films are fabricated utilizing atomic layerdeposition (ALD). In one embodiment, a tunnel dielectric for a magnetictunnel junction is formed by ALD. In another embodiment, thin metalfilms for magnetic devices are fabricated by ALD, such as by utilizingalternated metal source and hydrogen-rich plasma gases. In still anotherarrangement, thin metal films for magnetic devices are fabricated bydepositing metal oxide thin films by multiple ALD cycles, followed byreduction of the metal oxide to a metal state.

[0015] These methods ensure near perfect uniformity in magnetic andnon-magnetic conductors, and suppress migration that can cause spiking.In magnetic tunnel junction devices, dielectric layers of perfectuniformity allows optimal thickness, avoiding leakage current whilekeeping the layers thin enough to allow sensitivity for tunneling.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic cross section depicting the basic structureof a magnetic tunneling junction (MTJ) cell.

[0017]FIG. 2 is a schematic cross section depicting the structure of amagnetic tunneling cell, similar to that of FIG. 1, with additionallayers that cause an increased magnetic resistance effect.

[0018]FIG. 3 is a flow chart showing the basic pulsing sequence used fora two-phase atomic layer deposition (ALD) process.

[0019]FIG. 4 is a schematic cross-sectional drawing of a spin-valvetransistor.

[0020]FIG. 5 is a flow chart depicting a process for depositing aCo/Cu/Co structure by ALD.

[0021]FIG. 6 is a flow chart depicting a process for depositing aCo/AL₂O₃/Co structure by ALD.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] The present invention generally involves improvements in thefabrication of magnetic devices. The methods described herein may finduse, for example, in the formation of magnetic structures in memorycells (e.g., MRAMs) and the sensing elements of read-heads.

[0023] Magnetic Tunnel Junctions

[0024]FIG. 1, illustrates an integrated circuit device, and moreparticularly the magnetic tunnel junction (MTJ) of a magnetic randomaccess memory (MRAM) cell. The device includes two conductors,comprising ferromagnetic layers 12 and 16, and an insulator 14therebetween. Lines 10 and 18 represent electrodes on either side of thejunction. The insulator 14 serves as a tunneling dielectric layer 14 ofthe MTJ, sandwiched between a hard ferromagnetic layer 12 and a softferromagnetic layer 16.

[0025]FIG. 2 illustrates another example of an MRAM MTJ. In theillustrated embodiment, the device additionally includes layers 13 and15, which are conductors formed of a non-magnetic metal. In theillustrated embodiments layers 13 and 15 comprise copper.

[0026] Exemplary ALD processes are set forth hereinbelow, providingprocesses for forming the dielectric 14, the hard 14 and soft 16magnetic layers and the non-magnetic layers 13 and 15.

[0027] Al₂O₃ seems to be the best tunneling dielectric film so far.However, it has also been possible to deposit other dielectrics, such asSiO₂, Y₂O₃, La₂O₃, ZrO₂, HfO₂ and Ta₂O₅, by the ALD method.

[0028] As a further benefit of the ALD process, deposition of aluminumoxide by ALD onto a ferromagnetic metal surface does not oxidize theferromagnetic metal.

[0029] Formation of Magnetic Tunnel Junctions by Metal Oxide Depositionand Reduction

[0030] According to one aspect of the invention, the following processsteps are executed during the manufacturing of magnetic tunneljunctions.

[0031] A substrate comprising a hard magnetic material is provided. Thesubstrate surface is cleaned first by sputter-etching or by treatmentwith hydrogen-rich radicals, alcohols, aldehydes or carboxylic acids toeliminate any surface oxide in preparation for atomic layer deposition(ALD). Optionally, the cleaned metal layer may be treated prior todeposition of metal oxide to ensure the subsequent formation of auniform metal oxide layer by ALD on the substrate.

[0032] A first layer of metal oxide, such as cobalt oxide or copperoxide, is deposited, preferably by multiple cycles of ALD, onto thesubstrate. This first metal oxide layer is then reduced to elementalmetal. A thin tunneling dielectric layer, such as Al₂O₃, is deposited,preferably by ALD. A second metal oxide layer, such as cobalt oxide orcopper oxide, is deposited over the dielectric layer, preferably bymultiple cycles of ALD. The second metal oxide layer is then reduced toelemental metal.

[0033] An exemplary ALD process is illustrated in FIG. 6. A cobalt oxidelayer is deposited by ALD 200 and then reduced to elemental cobalt in areduction reaction 210. An aluminum oxide layer is then deposited by ALD220. Next a second cobalt oxide layer is deposited by ALD 230 over thealuminum oxide layer and reduced to elemental cobalt 240.

[0034] The formation of elemental metal layers by depositing a metaloxide and then reducing the metal oxide is beneficial to the formationof magnetic devices. The reduced mobility of the metal atoms in theoxide lowers the probability of island formation in the thin film duringdeposition and provides for more uniform film growth.

[0035] Formation of Magnetic Tunnel Junctions by Metal Deposition

[0036] Metal thin films can also be grown directly by ALD fromalternating pulses of volatile metal source chemicals and reducingagents. Preferably, the reducing phase is a very strong reducer,preferably rich in hydrogen radicals. Hydrogen-rich radicals can beproduced, for example, using an in situ plasma and more preferably aremote plasma source.

[0037] It is acceptable for the electrical resistance of a magnetictunnel junction (MTJ) to be quite high, so it is also possible to usesemi-metallic ferromagnetic materials for the ferromagnetic layers inmagnetic tunnel junctions. Materials such as Fe₃O₄ (magnetite), CrO₂,and manganite perovskites, which are preferably doped with alkalineearth metals, can be deposited by ALD and used in MTJ's instead ofelemental ferromagnetic metals. Suitable processes are discussed in“Thin film deposition of lanthanum manganite perovskite by the ALEprocess”, O. Nilsen, M. Peussa, H. Fjellvåg, L. Niinistö and A.Kjekshus, J. Mater. Chem. 9 (1999) 1781-1784, which is incorporated byreference herein.

[0038] ALD is a perfect tool for constructing unique magnetic metaloxide superlattices for use in magnetic tunnel junctions.

[0039] Spin Valve Transistor

[0040] With reference to FIG. 4, a spin-valve transistor is shown incross section. Electrical contacts are made to the transistor throughleads 30, 44 and 46. Electrons are injected from a silicon emitter 42into an exemplary base stack 41 that consists of four layers: platinum40, cobalt 38, copper 36 and cobalt 34. Electrons pass from the emitter42, through the base stack and into the silicon collector 32 to form thecollector current. The semiconductor-metal interfaces, 42/40, 34/32 areSchottky barriers. The exemplary base stack Pt/Co/Cu/Co 41 has a totalthickness of about 10 nm and, in the prior art, is usually deposited bysputtering. This stack 41 forms the base of the transistor. One or moreof the four layers of the stack 41 may be deposited by ALD.

[0041] Spin Valve Transistor Formation

[0042] The metal layers of the base stack 41 of the spin-valvetransistor can be deposited by plasma-enhanced atomic layer deposition(ALD) from alternating vapor phase pulses of metal source chemicals andhydrogen plasma.

[0043] More preferably, the magnetic layers 34, 38 and conductive layer36 of the base stack 41 are deposited in the form of metal oxides byALD, in accordance with the process of FIG. 5, steps 100 to 130.

[0044] As an option, a platinum oxide or cobalt-platinum oxide layer canalso be deposited by ALD on top of the second cobalt oxide layer.Subsequently, these metal oxide layers are chemically reduced toelemental metal layers with a reducing agent that is selected from thegroup consisting of, but not limited to, hydrogen, activated hydrogen,carbon monoxide, alcohols, aldehydes and carboxylic acids. Preferably,strong organic reducing agents are employed. The thickness of the metaloxide thin film decreases about 30-50% when oxygen is removed from thefilm during the reduction process.

[0045] A substrate with a patterned doped silicon surface, that willform a collector of electrons 32, is provided to the reaction chamber ofan ALD reactor. A first cobalt oxide layer is deposited 100 on thesubstrate from multiple cycles of alternate pulses of a cobalt sourcechemical and an oxygen source chemical. Copper oxide is deposited 110 onthe cobalt oxide surface from multiple cycles of alternating pulses of acopper source chemical and an oxygen source chemical. A second cobaltoxide layer is deposited 120 over the copper oxide from multiple cyclesof alternate pulses of a cobalt source chemical and an oxygen sourcechemical.

[0046] The oxides can be reduced 130 into metals using, for example,alcohols (e.g. ethanol), aldehydes (e.g. formaldehyde) or carboxylicacids (e.g. formic acid). The substrate with the oxide layers is placedin a reaction space that is subsequently evacuated. The reducing agentis vaporized and fed into the reaction space, optionally with the aid ofan inert carrier gas, such as nitrogen. The reducing agent reacts withthe oxide layers whereby the oxide trilayer structure, cobaltoxide/copper oxide/cobalt oxide, is chemically reduced to an elementaltrilayer structure, Co/Cu/Co. Typically, the reaction space is thenpurged with an inert carrier gas to remove the unreacted organicreducing agent and reaction products.

[0047] The reduction process can be carried out in a wide temperaturerange, even as low as room temperature. The temperature in the reactionspace is typically in the range of 250° C. to 400° C., preferably 300°C. to 400° C. and more preferably 310° C. to 390° C. The pressure in thereaction space is typically 0.01 mbar to 20 mbar. The processing timevaries according to the thickness of the layer to be reduced. A layer ofcopper oxide having a thickness up to 400 nm can be reduced inapproximately 3 to 5 minutes. For layers having a thickness of 0.1 nm to10 nm, the processing time is on the order of seconds. Typically, oxidelayer thickness decreases about 30% upon reduction to elemental metal.

[0048] To prevent reoxidation of the exposed cobalt top surface, thereduction is preferably done in the same reactor and just beforedeposition of the platinum metal. If reoxidation does occur, asubsequent reduction treatment using volatile organic compounds such asalcohols, aldehydes or carboxylic acids can be performed.

[0049] One benefit of depositing oxide films and later reducing thefilms to elemental form is that the mobility of the metal atoms isdecreased in the oxide form. This lowers the probability of islandformation in the thin film during deposition and ensures uniformtwo-dimensional film growth. Copper atoms, especially, have a tendencyfor high surface mobility even at room temperature.

[0050] Pseudo-spin Valve

[0051] According to another embodiment of the present invention one ormore layers in a pseudo-spin valve (not shown) can be constructed by themethods described herein. In a pseudo-spin valve, the firstferromagnetic layer is magnetically softer than the second ferromagneticlayer. A bit of information is stored in the first ferromagnetic layerand the second ferromagnetic layer helps to read the state of the firstferromagnetic layer. High-enough current will switch the magneticorientation of the first ferromagnetic layer, thus changing the storedone-bit information from 1 to 0 or 0 to 1. The operation of thepseudo-spin valve has been described in Scientific American, “In Focus:The Magnetic Attraction”, May 1999, the disclosure of which is includedherein by reference.

[0052] The first ferromagnetic (FM) layer can be made magneticallysofter than the second FM layer by using a different material that hashigher coercivity than the second FM layer. An example of thisdiffering-material structure is NiFe (first FM)/conductor/Co (secondFM). The cobalt layer can be pinned, for example with a Co₈₁Pt₁₉ alloylayer. Another possibility is to make both ferromagnetic layers of thesame material, but make the first FM layer thinner than the second one.An example of this differing-thickness structure is thin Co (firstFM)/conductor/thick Co (second FM). In both cases a conductive layerseparates the ferromagnetic layers. An exemplary material for theconductive layer is copper. In another arrangement the firstferromagnetic layer can be made harder than the second ferromagneticlayer.

[0053] Pseudo Spin Valve Formation by Metal Deposition

[0054] According to a first embodiment of the invention, the pseudo-spinvalve sandwich is formed by ALD with the use of metal source gases andhydrogen-rich radicals. The basic atomic layer deposition of each layerin the sandwich comprises the following steps:

[0055] (1) Metal source chemical vapor is introduced into the reactionspace and makes contact with the substrate surface.

[0056] (2) Surplus metal source chemical and reaction by-products arepurged from the reaction space by pumping and/or by flowing an inactivegas (e.g. nitrogen).

[0057] (3) Hydrogen-rich chemical plasma is introduced into the reactionspace and makes contact with the substrate surface.

[0058] (4) Surplus hydrogen-rich chemical plasma and reactionby-products are purged from the reaction space by pumping and/or byflowing inactive gas (e.g. nitrogen).

[0059] When a layer containing only one metal is required, the foursteps are repeated until the metal film reaches the desired thickness.As an example, a Co metal thin film is grown by ALD from volatilecompounds of cobalt and hydrogen plasma. The cobalt compoundself-limitingly adsorbs no more than about one monolayer of cobaltspecies on the substrate, while the hydrogen plasma reduces the adsorbedspecies to elemental metal.

[0060] When a layer containing a binary alloy is required, the foursteps are repeated alternately with a first metal source gas and asecond metal source gas until the alloy film reaches the desiredthickness.

[0061] As a non-limiting example, the completed sandwich may contain 6nm NiFe/5 nm Cu/6 nm Co. As another, non-limiting example, the completedsandwich may contain 6 nm Co 5 nm Cu 20 nm Co.

[0062] Benefits of these ALD processes include the fact that all theprocess steps can be done at low substrate temperatures and the controlover the thin film thickness uniformity is excellent.

[0063] Pseudo Spin Valve Formation by Deposition of Metal Oxide Followedby Reduction

[0064] In accordance with another embodiment of the invention, metaloxides are first deposited, preferably by multiples cycles of ALD, andthen these metal oxide layers are reduced into elemental metal layers.In this case, atomic layer deposition of each layer in the sandwichcomprises a cycle of the following steps:

[0065] (1) Metal source chemical vapor is introduced into the reactionspace and makes contact with the substrate surface.

[0066] (2) Surplus metal source chemical and reaction by-products arepurged from the reaction space by pumping and/or by flowing an inactivegas (e.g. nitrogen).

[0067] (3) Oxygen source chemical is introduced into the reaction spaceand makes contact with the substrate surface.

[0068] (4) Surplus oxygen source chemical and reaction by-products arepurged from the reaction space by pumping and/or by flowing an inactivegas (e.g. nitrogen).

[0069] These four steps are repeated for many cycles until a metal oxidethin film of desired thickness is formed. As an example, a cobalt oxidethin film is grown by ALD from volatile compounds of cobalt (e.g.Co(thd)₃) and volatile or gaseous oxygen compounds (e.g. ozone).

[0070] After finishing the ALD processing, there are metal oxide layerson the substrate surface. As a non-limiting example, the layers maycontain 9 nm cobalt oxide/8 nm copper oxide/25 nm cobalt oxide. Theoxide stack can be reduced into an elemental metal stack(cobalt/copper/cobalt) in one step. Hydrogen gas, hydrogen-rich plasma,carbon monoxide, alcohols, aldehydes and some carboxylic acids can beused, for example, as reducing agents to effect the transformation.

[0071] One benefit of this “metals from metal oxide” process is that thesurface mobility of metal atoms is reduced when they are bound tooxygen. This decreases the chances of agglomeration and island formationduring deposition and helps to ensure thickness uniformity andconsistency in the thin-film growth. In the as-deposited structure, theoxide layers are separate and distinct from one another with planarinterfaces in between. Another benefit of this “metals from metal oxide”process is that the deposition steps and the reducing steps can beperformed at low temperatures, e.g., less than 300° C., which isdesirable in integrated circuit fabrication. ALD provides excellentcontrol over the thin film thickness uniformity.

[0072] The Deposition Process

[0073] For the purpose of the present invention, an atomic layerdeposition (ALD) process, also known as atomic layer epitaxy (ALE),designates a process where the deposition of a thin film onto asubstrate is based on sequential and alternating self-saturating surfacereactions from at least two separate gaseous source chemicals.Temperatures are arranged to be above the condensation points and belowthe thermal decomposition points for the source chemicals. Theprinciples of ALD are disclosed, for example, in U.S. Pat. Nos.4,058,430 and 5,711,811, the disclosures of which are incorporatedherein by reference. A thorough description of the ALD process can befound in “Atomic Layer Epitaxy” by Dr. Tuomo Suntola, Handbook ofCrystal Growth vol. 3, Thin films and Epitaxy, Part B: Growth Mechanismsand Dynamics, Chapter 14, pp. 601-663, Edited by D. T. J. Hurle,Elsevier Science B.V., 1994, the disclosure of which is included hereinby reference.

[0074]FIG. 3 depicts a basic two-phase process for atomic layerdeposition. Source chemical pulses 40 and 44 are separated from oneanother in time and space by purge periods 42 and 46. Alternatively, thepurge periods can be replaced by evacuation of the chamber to removebyproduct and excess reactant between source chemical pulses 40, 44.Importantly, each pulse preferably has a self-limiting effect, leavingno more than about one molecular monolayer of material per cycle.Typically, the metal source chemicals include ligands thatself-terminate adsorption of a monolayer or partial monolayer.

[0075] The Source Materials

[0076] ALD requires thermally stable source chemicals that havehigh-enough vapor pressure at the source temperature (preferably 200° C.to 400° C., 300° C. in the illustrated embodiments). Sufficiently highvapor pressure of the source chemical is around 0.01-0.1 mbar. Highervapor pressure can decrease the required minimum pulse time of thesource chemical and make the process faster.

[0077] Metal Source Materials

[0078] Volatile aluminum source chemicals are selected from the groupconsisting of, but not limited to, alkyl aluminums (e.g. trimethylaluminum TMA), aluminum alkoxides (e.g. aluminum isopropoxide(Al(O^(i)Pr)₃)), aluminum beta-diketonates (e.g. Al(thd)₃) and anhydrousaluminum nitrate (Al(NO₃)₃).

[0079] Volatile copper compounds are selected from the group consistingof, but not limited to, Cu(thd)₂, Cu(acac)₂, Cu(hfac)₂, CuCl, CuBr, CuIand anhydrous copper nitrate (Cu(NO₃)₂). Anhydrous Cu(NO₃)₂ has not beencommercially available but it can easily be synthesized from coppermetal and dinitrogen tetroxide in anhydrous ethyl acetate. The synthesishas been described by C. C. Addison and B. J. Hathaway, “The VaporPressure of Anhydrous Copper Nitrate, and its Molecular Weight in theVapor State”, J. Chem. Soc. 1958 pp. 3099-3106, the disclosure of whichis included herein by reference.

[0080] Volatile cobalt compounds are selected from the group consistingof, but not limited to,tris(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt (Co(thd)₃),Co(acac)₃, cobalt tricarbonyl nitrosyl (Co(CO)₃NO),cyclopentadienylcobalt dicarbonyl (C₅H₅Co(CO)₂) and anhydrous cobaltnitrate (Co(NO₃)₃). Anhydrous cobalt nitrate (Co(NO₃)₃) has not beencommercially available but it can be synthesized, e.g., according to theinstruction published by R. J. Fereday, N. Logan and D. Sutton,“Anhydrous cobalt(III) nitrate”, Chem. Commun. 1968, pp. 271, thedisclosure of which is included herein by reference.

[0081] Volatile iron compounds are selected from the group consistingof, but not limited to, tris(2,2,6,6-tetramethyl-3,5-heptanedionato)iron(Fe(thd)₃), bis(cyclopentadienyl)iron ((C₅H₅)₂Fe) and its alkylderivatives, iron (III) acetylacetonate (Fe(CH₃COCHCOCH₃)₃), iron (III)chloride (FeCl₃) and iron pentacarbonyl (Fe(CO)₅).

[0082] Volatile chromium compounds are selected from the groupconsisting of, but not limited to,tris(2,2,6,6-tetramethyl-3,5-heptanedionato)chromium (Cr(thd)₃), chromylchloride (CrO₂Cl₂), bis(cyclopentadienyl)chromium ((C₅H₅)₂Cr) and itsalkyl derivatives, bis(ethylbenzene)chromium, chromium (III)acetylacetonate (Cr(CH₃COCHCOCH₃)₃) and chromium hexacarbonyl (Cr(CO)₆).

[0083] Volatile nickel compounds are selected from the group consistingof, but not limited to,bis(2,2,6,6-tetramethyl-3,5-heptanedionato)nickel (Ni(thd)₂), nickelcarbonyl (Ni(CO)₄), nickel (II) hexafluoroacetylacetonate,bis(cyclopentadienyl)nickel ((C₅H₅)₂Ni) and its alkyl derivatives andtetrakis(trifluorophosphine)nickel (0) (Ni(PF₃)₄).

[0084] Oxygen Source Materials

[0085] Gaseous or volatile oxygen source chemicals can be selected fromthe group consisting of, but not limited to, oxygen, ozone, water,hydrogen peroxide, peroxy acids (e.g. CH₃COOOH), and oxygen radicals.

[0086] Post ALD Reducing Agents

[0087] As used herein, the terms “reduction” and “reducing” refer to theremoval of oxygen atoms from a metal layer. “Reduction” does not have tobe complete reduction and some oxygen atoms may remain in a metal layerafter it has been reduced. Thus a metal layer that is “reduced” or “atleast partially reduced” is a metal layer from which some, but notnecessarily all oxygen atoms have been removed. Further, an “elementalmetal” that is formed by “reduction” of a metal oxide is a metal layerfrom which most oxygen atoms have been removed. However, it isunderstood that an elemental metal layer may contain some residual orcontaminant oxygen atoms.

[0088] Reducing agents can be selected from, but are not limited to, thefollowing: hydrogen, hydrogen-rich radicals, carbon monoxide, alcoholvapor, aldehyde vapor and carboxylic acid vapor.

[0089] In one embodiment metal oxide is reduced with hydrogen plasma.Briefly, the substrate comprising the metal oxide layer is placed in areaction chamber. A gas mixture comprising hydrogen is allowed to flowinto the reaction chamber and Radio Frequency (RF) power is applied tocreate a plasma discharge in the hydrogen gas. The plasma dischargeetches the metal oxide, leaving elemental metal.

[0090] In another embodiment metal oxide layers are reduced with one ormore organic reducing agents. Preferably the organic reducing agentshave at least one functional group selected from the group consisting ofalcohol, aldehyde and carboxylic acid.

[0091] Reducing agents containing at least one alcohol group arepreferably selected from the group consisting of primary alcohols,secondary alcohols, tertiary alcohols, polyhydroxy alcohols, cyclicalcohols, aromatic alcohols, halogenated alcohols, and other derivativesof alcohols.

[0092] Preferred primary alcohols have an —OH group attached to a carbonatom that is bonded to another carbon atom, in particular primaryalcohols according to the general formula (1):

R¹—OH   (I)

[0093] wherein R¹ is a linear or branched C₁-C₂₀ alkyl or alkenylgroups, preferably methyl, ethyl, propyl, butyl, pentyl or hexyl.Examples of preferred primary alcohols include methanol, ethanol,propanol, butanol, 2-methyl propanol and 2-methyl butanol.

[0094] Preferred secondary alcohols have an —OH group attached to acarbon atom that is bonded to two other carbon atoms. In particular,preferred secondary alcohols have the general formula (II):

[0095] wherein each R¹ is selected independently from the group oflinear or branched C₁-C₂₀ alkyl and alkenyl groups, preferably methyl,ethyl, propyl, butyl, pentyl or hexyl. Examples of preferred secondaryalcohols include 2-propanol and 2-butanol.

[0096] Preferred tertiary alcohols have an -OH group attached to acarbon atom that is bonded to three other carbon atoms. In particular,preferred tertiary alcohols have the general formula (III):

[0097] wherein each R¹ is selected independently from the group oflinear or branched C₁-C₂₀ alkyl and alkenyl groups, preferably methyl,ethyl, propyl, butyl, pentyl or hexyl. An example of a preferredtertiary alcohol is tert-butanol.

[0098] Preferred polyhydroxy alcohols, such as diols and triols, haveprimary, secondary and/or tertiary alcohol groups as described above.Examples of preferred polyhydroxy alcohol are ethylene glycol andglycerol.

[0099] Preferred cyclic alcohols have an —OH group attached to at leastone carbon atom which is part of a ring of 1 to 10, more preferably 5-6carbon atoms.

[0100] Preferred aromatic alcohols have at least one —OH group attachedeither to a benzene ring or to a carbon atom in a side chain. Examplesof preferred aromatic alcohols include benzyl alcohol, o-, p- andm-cresol and resorcinol.

[0101] Preferred halogenated alcohols have the general formula (IV):

CH_(n)X_(3−n)—R²—OH   (IV)

[0102] wherein X is selected from the group consisting of F, Cl, Br andI, n is an integer from 0 to 2 and R² is selected from the group oflinear or branched C₁-C₂₀ alkyl and alkenyl groups, preferably methyl,ethyl, propyl, butyl, pentyl or hexyl. More preferably X is selectedfrom the group consisting of F and Cl and R² is selected from the groupconsisting of methyl and ethyl. An example of a preferred halogenatedalcohol is 2,2,2-trifluoroethanol.

[0103] Other preferred derivatives of alcohols include amines, such asmethyl ethanolamine.

[0104] Preferred reducing agents containing at least one aldehyde group(—CHO) are selected from the group consisting of compounds having thegeneral formula (V), alkanedial compounds having the general formula(VI), halogenated aldehydes and other derivatives of aldehydes.

[0105] Thus, in one embodiment preferred reducing agents are aldehydeshaving the general formula (V):

R³—CHO   (V)

[0106] wherein R³ is selected from the group consisting of hydrogen andlinear or branched C₁-C₂₀ alkyl and alkenyl groups, preferably methyl,ethyl, propyl, butyl, pentyl or hexyl. More preferably, R³ is selectedfrom the group consisting of methyl or ethyl. Examples of preferredcompounds according to formula (V) are formaldehyde, acetaldehyde andbutyraldehyde.

[0107] In another embodiment preferred reducing agents are aldehydeshaving the general formula (VI):

OHC—R⁴—CHO   (VI)

[0108] wherein R⁴ is a linear or branched C₁-C₂₀ saturated orunsaturated hydrocarbon. Alternatively, the aldehyde groups may bedirectly bonded to each other (R⁴ is null).

[0109] Preferred reducing agents containing at least one —COOH group arepreferably selected from the group consisting of compounds of thegeneral formula (VII), polycarboxylic acids, halogenated carboxylicacids and other derivatives of carboxylic acids.

[0110] Thus, in one embodiment preferred reducing agents are carboxylicacids having the general formula (VII):

R⁵—COOH   (VII)

[0111] wherein R⁵ is hydrogen or linear or branched C₁-C₂₀ alkyl oralkenyl group, preferably methyl, ethyl, propyl, butyl, pentyl or hexyl,more preferably methyl or ethyl. Examples of preferred compoundsaccording to formula (VII) are formic acid and acetic acid, mostpreferably formic acid (HCOOH).

EXAMPLE 1 The Deposition of Aluminum Oxide by ALD

[0112] A substrate was loaded into a reactor configured for ALDprocessing. The reaction space was evacuated with a vacuum pump. Afterthe evacuation, the pressure of the reaction space was adjusted to about5-10 mbar (absolute) with flowing nitrogen gas that had a purity of99.9999%. Then the reaction chamber was allowed to stabilize at 300° C.Alternating pulses of trimethyl aluminum (TMA) and water were introducedinto the reaction space and made contact with the substrate surface. Thereaction space was purged with nitrogen gas between the alternatingpulses.

[0113] The growth rate of the amorphous Al₂O₃ film was 0.11 nm/cycle.The thickness variation of an aluminum oxide film was less than 1%.Advantageously, Al₂O₃ is thermodynamically stable and tends not to causeoxidation of the adjacent metal layers.

EXAMPLE 2 The Deposition of Copper Oxide by ALD and a Reducing Method

[0114] The deposition of copper oxide by ALD and its subsequentreduction to copper metal is described in Finnish patent application no.FI20001163, filed May 15, 2000, now abandoned, PCT application numberFI01/00473, filed May 15, 2001 and U.S. patent application Ser. No.09/975,466, filed Oct. 9, 2001, the disclosures of which are includedherein by reference.

[0115] A. Reduction of CuO with Methanol Vapor

[0116] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor, commercially available fromASM Japan. The reaction chamber is evacuated to vacuum and heated to360° C. The pressure of the reaction chamber is adjusted to about 5-10mbar with flowing nitrogen gas.

[0117] Methanol vapor is mixed with nitrogen gas, introduced to thereaction chamber and contacted with the substrate.

[0118] Excess methanol and reaction by-products are purged from thereaction chamber by flowing nitrogen gas.

[0119] B. Reduction of CuO with Ethanol Vapor

[0120] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum and heated to 360° C. The pressure of the reactionchamber is adjusted to about 5-10 mbar with flowing nitrogen gas.

[0121] Ethanol vapor is mixed with nitrogen gas, introduced to thereaction chamber and contacted with the substrate.

[0122] Excess ethanol and reaction by-products are purged from thereaction chamber by flowing nitrogen gas.

[0123] C. Reduction of CuO with 2-Propanol Vapor

[0124] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum and heated to 360° C. The pressure of the reactionchamber is adjusted to about 5-10 mbar with flowing nitrogen gas.

[0125] 2-propanol (also known as isopropanol) vapor is mixed withnitrogen gas, introduced to the reaction chamber and contacted with thesubstrate.

[0126] Excess 2-propanol and reaction by-products are purged from thereaction chamber by flowing nitrogen gas.

[0127] D. Reduction of CuO with tert-Butanol Vapor

[0128] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum and heated to greater than 385° C. The pressure ofthe reaction chamber is adjusted to about 5-10 mbar with flowingnitrogen gas.

[0129] Tert-butanol vapor is mixed with nitrogen gas, introduced to thereaction chamber and contacted with the substrate.

[0130] Excess tert-butanol and reaction by-products are purged from thereaction chamber by flowing nitrogen gas.

[0131] E. Reduction of CuO with Butyraldehyde Vapor

[0132] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum and heated to 360° C. The pressure of the reactionchamber is adjusted to about 5-10 mbar with flowing nitrogen gas.

[0133] Butyraldehyde vapor is mixed with nitrogen gas, introduced to thereaction chamber and contacted with the substrate.

[0134] Excess butyraldehyde and reaction by-products are purged from thereaction chamber by flowing nitrogen gas.

[0135] F. Reduction of CuO with Formic Acid Vapor

[0136] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum and heated to 310° C. The pressure of the reactionchamber is adjusted to about 5-10 mbar with flowing nitrogen gas.

[0137] Formic acid vapor is mixed with nitrogen gas, introduced to thereaction chamber and contacted with the substrate.

[0138] Excess formic acid and reaction by-products are purged from thereaction chamber by flowing nitrogen gas.

[0139] G. Reduction of CuO with Acetic Acid Vapor

[0140] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum and heated to 360° C. The pressure of the reactionchamber is adjusted to about 5-10 mbar with flowing nitrogen gas.

[0141] Acetic acid vapor is mixed with nitrogen gas, introduced to thereaction chamber and contacted with the substrate.

[0142] Excess acetic acid and reaction by-products are purged from thereaction chamber by flowing nitrogen gas.

[0143] H. Reduction of CuO with Plasma

[0144] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum and heated to approximately 300° C. The pressure ofthe reaction chamber is adjusted to about 5-10 mbar with flowing gascomprising hydrogen.

[0145] A plasma discharge or glow is created in the gas by theapplication of RF power. Plasma treatment is continued for approximately2 minutes.

[0146] Reaction byproducts are purged from the reaction chamber withflowing nitrogen gas.

[0147] I. Reduction of CuO with Hydrogen

[0148] A substrate comprising a copper oxide layer is loaded into thereaction chamber of an Eagle 10™ reactor. The reaction chamber isevacuated to vacuum, heated to approximately 500° C. and the pressure ofthe reaction chamber is adjusted to about 5-10 mbar with flowingnitrogen gas.

[0149] Hydrogen gas is mixed with nitrogen gas (10% hydrogen by volume),introduced to the reaction chamber and contacted with the substrate.

[0150] Reaction byproducts are purged from the reaction chamber withflowing nitrogen gas.

EXAMPLE 3 The Deposition of Cobalt Oxide by ALD and a Reducing Method

[0151] Cobalt oxide (CoO) was deposited by ALD from alternating pulsesof Co(thd)₃ and an ozone/oxygen mixture. A substrate was loaded into thereaction space of an ALD reactor. The reaction space was evacuated witha vacuum pump. The reaction space temperature was adjusted to 250° C.Cobalt source gas Co(thd)₃ was heated to 110° C. in a source containerinside the ALD reactor. Alternating pulses of cobalt source gas and theozone/oxygen mixture were introduced into the reaction space. Theozone/oxygen mixture had a flow rate of about 100 std. cm³/min duringthe ozone pulse.

[0152] The pulsing cycle consisted of the following steps:

[0153] Co(thd)₃ pulse 1.5 s

[0154] N₂ purge 2.0 s

[0155] O₃ pulse 3.0 s

[0156] N₂ purge 2.0 s.

[0157] The pulsing cycle was repeated 2000 times. The resulting thinfilm had a thickness of about 64 nm and a growth rate of about 0.03nm/cycle. Stoichiometry of the CoO film was determined by energydispersive x-ray spectroscopy (EDS).

[0158] CoO was reduced into Co metal by treating the samples withethanol vapor for 10 minutes at 400° C. Energy dispersive x-rayspectroscopy (EDS) results showed that the reduced film was pure cobalt;the oxygen content of the cobalt film was below the detection limit ofthe EDS. The above process was successfully employed to deposit layersof 200 nm to metal. It will be understood that, for layers in the rangedesired for the preferred magnetic devices, the reduction temperaturecan be lowered, e.g., to the 300° C. process temperature of the ALDprocesses.

[0159] Regarding the ferromagnetic layers, reduction of metal oxide intometal was tested with cobalt oxide, as described above in Example 3.Reduction of nickel oxide into nickel metal is also possible. Thereduction of platinum oxide into platinum metal is also possible for theproduction of a pinning layer. Reduction of iron oxide into iron metalrequires quite strong reducing agent. A relatively good correlationbetween theoretical calculations (Free Gibb's energy of the reaction,calculated with HSC Chemistry® for Windows, Outokumpu Research Oy,Finland) and experiments for the reduction process has been observed.

[0160] Although the foregoing invention has been described in terms ofcertain preferred embodiments, other embodiments will be apparent tothose of ordinary skill in the art. Additionally, other combinations,omissions, substitutions and modification will be apparent to theskilled artisan, in view of the disclosure herein. Accordingly, thepresent invention is not intended to be limited by the recitation of thepreferred embodiments, but is instead to be defined by reference to theappended claims.

We claim:
 1. A method of fabricating a magnetic memory cell, comprising:providing a substrate on which the magnetic memory cell is formed;depositing a first ferromagnetic layer; depositing a dielectric layerover the first ferromagnetic layer; and depositing a secondferromagnetic layer over the dielectric layer, wherein at lease one ofthe layers is formed by atomic layer deposition (ALD).
 2. The method ofclaim 1, wherein the magnetic memory cell comprises a magnetic tunnelingjunction (MTJ).
 3. The method of claim 1, wherein the magnetic memorycell is a magnetic random access memory cell.
 4. The method of claim 1,wherein the dielectric layer is deposited by ALD.
 5. The method of claim1, wherein the dielectric layer comprises aluminum oxide.
 6. The methodof claim 1, wherein the first ferromagnetic layer is deposited by ALD.7. The method of claim 6, wherein depositing the first ferromagneticlayer by ALD comprises depositing a metal oxide by ALD and subsequentlyreducing the metal oxide to elemental metal.
 8. The method of claim 7,wherein the elemental metal comprises cobalt.
 9. The method of claim 1,wherein depositing the second ferromagnetic layer comprises an ALDprocess.
 10. The method of claim 9, wherein depositing the secondferromagnetic layer comprises depositing a metal oxide by ALD andsubsequently reducing the metal oxide to elemental metal.
 11. The methodof claim 10, wherein the elemental metal comprises cobalt.
 12. Themethod of claim 1, wherein the first ferromagnetic layer has a lowermagnetic permeability than the second ferromagnetic layer.
 13. Themethod of claim 1, wherein the first ferromagnetic layer is thinner thanthe second ferromagnetic layer.
 14. A method of fabricating a magneticmemory cell, comprising: providing a substrate on which the magneticmemory cell is formed; depositing a first magnetic layer on thesubstrate; forming a dielectric layer over the first magnetic layer;depositing a magnetic metal oxide layer over the dielectric layer byatomic layer deposition (ALD); and reducing the magnetic metal oxidelayer to a magnetic elemental metal layer.
 15. A method of fabricating amagnetic memory cell, comprising: providing a substrate on which themagnetic memory cell is formed; forming a first magnetic layer on thesubstrate; depositing a first non-magnetic metal oxide layer over thefirst magnetic layer; converting the first non-magnetic metal oxidelayer to a first non-magnetic metal layer; depositing an insulatinglayer on the first non-magnetic metal layer; depositing a secondnon-magnetic metal oxide layer by atomic layer deposition (ALD);converting the second non-magnetic metal oxide layer to a secondnon-magnetic metal layer; and depositing a second magnetic layer on thesecond non-magnetic metal layer.
 16. The method of claim 15, wherein thefirst non-magnetic metal oxide layer is deposited by ALD.
 17. The methodof claim 15, wherein the first non-magnetic metal oxide layer and thesecond non-magnetic metal oxide layer are converted to the first andsecond non-magnetic metal layers by reducing the metal oxide toelemental metal.
 18. The method of claim 17, wherein reducing comprisesexposing the metal oxide layer to a chemical selected from the groupconsisting of hydrogen, hydrogen-rich radicals, carbon monoxide, alcoholvapor, aldehyde vapor and carboxylic acid vapor.
 19. The method of claim15, wherein the first and the second non-magnetic metal oxide layerscomprise copper oxide.
 20. A method of fabricating a magneticnanolaminate structure, comprising: depositing a plurality of metaloxide layers on a substrate by atomic layer deposition (ALD); andconverting at least one of the metal oxide layers to elemental metallayers, wherein at least one of the metal oxide layers is magnetic. 21.The method of claim 20, wherein the magnetic nanolaminate structure ispart of a magnetic memory device.
 22. The method of claim 20, whereinthe magnetic nanolaminate structure is part of a read-head.
 23. Themethod of claim 20, wherein the magnetic nanolaminate structurecomprises a magnetic tunneling junction.
 24. The method of claim 20,wherein the magnetic nanolaminate structure is part of a spin valvetransistor.
 25. The method of claim 20, wherein depositing the pluralityof metal oxide layers comprises, in order: depositing a first magneticmetal oxide layer, depositing an insulating layer, and depositing asecond magnetic metal oxide layer.
 26. The method of claim 20, whereindepositing the plurality of metal oxide layers comprises, in order:depositing a first magnetic metal oxide layer, depositing a firstnon-magnetic metal oxide layer, depositing an insulating layer,depositing a second non-magnetic metal oxide layer, and depositing asecond magnetic metal oxide layer.
 27. The method of claim 20, whereinconverting comprises reducing a metal oxide layer to elemental metal.28. The method of claim 27, wherein reducing comprises contacting thelayer with a compound selected from the group consisting of hydrogen,hydrogen-rich radicals, carbon monoxide, alcohol vapor, aldehyde vaporand carboxylic acid vapor.
 29. The method of claim 20, wherein at leastone of the metal oxide layers comprises a ferromagnetic oxide selectedfrom the group consisting of magnetite (Fe₃O₄), CrO₂, manganiteperovskites doped with alkaline earth metals and metal oxidesuperlattices.
 30. The method of claim 20, wherein the magneticnanolaminate comprises at least one magnetic metal selected from thegroup consisting of iron (Fe), cobalt (Co) and nickel (Ni).
 31. Themethod of claim 20, wherein the magnetic nanolaminate comprises at leastone non-magnetic metal.
 32. The method of claim 31, wherein thenon-magnetic metal is copper.
 33. A method of depositing a metal layerfor a magnetic device by atomic layer deposition (ALD), wherein the ALDprocess comprises alternately contacting a substrate with volatile metalsource chemicals and hydrogen-rich plasma.
 34. The method of claim 33,wherein the ALD process forms a metal oxide.
 35. The method of claim 34,further comprising reducing the metal oxide.
 36. The method of claim 34,wherein the metal oxide comprises a magnetic metal.
 37. The method ofclaim 36, wherein the magnetic metal is selected from the groupconsisting of iron (Fe), cobalt (Co) and nickel (Ni).
 38. The method ofclaim 34, wherein the metal oxide comprises a non-magnetic metal. 39.The method of claim 33, wherein the magnetic device comprises anintegrated MRAM magnetic tunnel junction.
 40. The method of claim 33,wherein the magnetic device comprises a spin valve transistor.
 41. Themethod of claim 33, wherein, the magnetic device comprises a pseudo spinvalve.
 42. A method of manufacturing a magnetic element in an integratedcircuit, comprising: providing a substrate comprising a hard magneticmaterial; cleaning the substrate surface; depositing an aluminum oxidetunneling dielectric by atomic layer deposition (ALD) on the substrate;depositing cobalt oxide over the aluminum oxide by ALD; and reducing thecobalt oxide to cobalt metal.
 43. The method of claim 42, whereincleaning comprises sputter-etching.
 44. The method of claim 42, whereincleaning comprises contacting the substrate surface with a gas selectedfrom the group consisting of hydrogen, hydrogen-rich radicals, carbonmonoxide, alcohol vapor, aldehyde vapor and carboxylic acid vapor. 45.The method of claim 42, wherein reducing the cobalt oxide comprisescontacting the substrate with a gas selected from the group consistingof hydrogen, hydrogen-rich radicals, carbon monoxide, alcohol vapor,aldehyde vapor and carboxylic acid vapor. A method of reducing oxidizedferromagnetic metal in a magnetic structure into elemental metalcomprising contacting the oxidized metal with a volatile organiccompound selected from the group consisting of alcohols, aldehydes andcarboxylic acids.
 46. A method of fabricating a sensing element of aread-head comprising: providing a substrate on which the sensing elementis to be formed; depositing a first ferromagnetic layer by atomic layerdeposition (ALD); depositing a conductive layer over the firstferromagnetic layer; and depositing a second ferromagnetic layer overthe conductive layer.
 47. The method of claim 46, wherein the conductivelayer is deposited by atomic layer deposition.
 48. The method of claim46, wherein the second ferromagnetic layer is deposited by atomic layerdeposition.
 49. The method of claim 46, wherein the first ferromagneticlayer comprises NiFe and the second ferromagnetic layer comprises Co.50. The method of claim 46, wherein the conductive layer comprises Cu.